1. Field of the Invention
The present invention relates to a fuel tank diagnostic apparatus.
2. Description of the Related Art
If there is a space above the surface of liquid fuel in a fuel tank, fuel evaporates into the space, and fuel vapor may escape from the fuel tank into the atmosphere. Japanese Patent Application Laid-Open No. HEI 7-132738 discloses a fuel tank equipped with an expandable-shrinkable air bag that is expanded or shrunk in accordance with changes in the level of the surface of liquid fuel in the fuel tank so that the air bag always remains in close contact with the surface of liquid fuel.
In the fuel tank disclosed in the Japanese Patent Application Laid-Open No. HEI 7-132738, the interior space of the air bag is in communication with a fuel vapor adsorbing canister so that fuel vapor allowed to permeate through the air bag sheet will not escape to the atmosphere.
If the air bag in the fuel tank as described in Japanese Patent Application Laid-Open No. HEI 7-132738 repeatedly expands and shrinks, a hole may be formed in the air bag material, or the air bag material may come to swell with fuel or may come to allow passage of fuel therethrough. If such an undesired event happens, it is necessary to detect that the fuel tank has a failure. However, the aforementioned conventional fuel tank does not have a function to detect a fault or failure in the fuel tank.